So if the Holy Spirit was indeed within the pillar of cloud by day, we would expect to see some kind of parallel in the New Testament.
Clouds are made up of a different form of water and they release water (rain):
John 7:37-39
"In the last day, that great day of the feast, Jesus stood and cried, saying, If any man thirst, let him come unto me, and drink. He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water. (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.)"
If the Holy Spirit was indeed within the pillar of fire by night, we should expect to see some kind of parallel in the New Testament.
Acts of the Apostles 2:3-4
"And there appeared unto them cloven tongues like as of fire, and it sat upon each of them. And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance."
So what about the part about how they are guided by night by the light of the pillar of fire?
Scripture is inspired by the Holy Spirit (2 Peter 1:20-21) (2 Timothy 3:16) (Ephesians 6:17).
So God's Word (the Bible) inspired by the Spirit leads us like a light while we are in this world of darkness.
Thy word is a lamp.
"Thy word is a lamp unto my feet, and a light unto my path." (Psalms 119:105).
As the Spirit guides us with His Word in this dark world to God's Kingdom, the Israelite was guided by the Spirit with the pillar of cloud by day, and the pillar of fire by night to the Promised Land.
Also, why a pillar? Do we see a pillar in the New Testament?
"But if I tarry long, that thou mayest know how thou oughtest to behave thyself in the house of God, which is the church of the living God, the pillar and ground of the truth." (1 Timothy 3:15).
The church is the body of Christ formed around the truth of Scripture.
(Note: Jesus said to God the Father in prayer, "Sanctify them with your truth, your word is Truth."). The church are a people. They are the temple of the living God.
"Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?" (1 Corinthians 3:16).
Interesting how the church is referred to as a pillar in 1 Timothy 3:15 and yet 1 Corinthians 3:16 says we are the temple of the Holy Spirit.
So if the church is called a pillar by which the Spirit is to dwell in like a temple, it could also be possible that the shape of the cloud (i.e. the pillar of cloud by day), and the shape of the fire (i.e. the pillar of fire by night) could be representative of the covering for the Holy Spirit guiding the Israelites to the Promised Land.